1. Field of the Invention
The present invention relates to more reliable solid electrolytic capacitor with a larger capacitance, and a method of manufacturing the same.
2. Description of Related Art
Solid electrolytic capacitors exhibit good high-frequency characteristics, and have large capacities although small in size. For this reason, solid electrolytic capacitors are widely used for power supply circuits in various electronic appliances including personal computers and imaging devices. In addition, the emergence of higher-performance mobile appliances typified by cellular phones and portable music players demands smaller-sized capacitors with higher capacitances.
FIG. 5A is a cross-sectional view of a conventional solid electrolytic capacitor. FIG. 5B is a cross-sectional view of the solid electrolytic capacitor taken along line B-B of FIG. 5A. FIG. 5C is a cross-sectional view of the solid electrolytic capacitor taken along line C-C of FIG. 5A. As shown in FIGS. 5A to 5C, anode body 3, dielectric layer 4, and conducting polymer layer 5 are formed around anode lead 2. Surrounding anode lead 2, anode body 3 is formed by sintering particles of a valve metal such as tantalum, niobium, titanium and aluminum into a cuboid shape.
Dielectric layer 4 is formed on the respective surfaces of anode body 3 and anode lead 2. Dielectric layer 4 is formed by oxidizing the respective surfaces of anode body 3 and anode lead 2, for example, by anodization. Conducting polymer layer 5 made of a conducting polymer such as polypyrrole and polyaniline is formed on the dielectric layer 4 and in spaces in a way that the spaces are embedded with conducting polymer layer 5.
Carbon layer 6 and silver layer 7 are formed on the top surface of conducting polymer layer 5. Anode terminal 1, which is plate-shaped, is connected to anode lead 2, whereas cathode terminal 8, which is plate-shaped, is connected to silver layer 7.
Outer package 9 is formed in a cuboid shape in order to accommodate anode lead 2, anode body 3, dielectric layer 4, conducting polymer layer 5, carbon layer 6 and silver layer 7. Outer package 9 is formed, for example, from an epoxy resin. Anode terminal 1 and cathode terminal 8 are drawn out of the outer package 9, and extend in mutually different directions, and are bent downwards. Extremity portions respectively of these terminals are arranged along the bottom surface of outer package 9, and are used to electrically connect the solid electrolytic capacitor to a mount substrate. A solid electrolytic capacitor with this configuration is disclosed, for example, in Japanese Patent Application Laid-Open Publication No. 2004-14667.
In making a solid electrolytic capacitor with a larger capacitance, the surface area of a sintered body is increased, which is used as the anode body, and which is obtained by sintering metal particles made of a valve metal or its alloy around the anode lead. A method of increasing the surface area of the sintered body includes increasing the particle density by reducing the size of metal particles used for sintering.